Yves wrote:Hm, if you have an imbalance between cylinders, how do you know it's either fuel or ignition related when you have to rely on egt's ?

You don't know. That's where your individual EGOs have an edge. However at the same time if you have an ignition timing imbalance between cylinders that's large enough to really influence EGT then you would be wasting your time performing any form of basic calibration not to mind something as far along the line as fuel trims.

Obviously knock control would be a case where ignition imbalance cant be helped is during knock control so for that reason you can't use any EGT data for fuel trims if one or more cylinders have knock control active.

Yves wrote:Hm, if you have an imbalance between cylinders, how do you know it's either fuel or ignition related when you have to rely on egt's ?

You don't know. That's where your individual EGOs have an edge. However at the same time if you have an ignition timing imbalance between cylinders that's large enough to really influence EGT then you would be wasting your time performing any form of basic calibration not to mind something as far along the line as fuel trims.

Obviously knock control would be a case where ignition imbalance cant be helped is during knock control so for that reason you can't use any EGT data for fuel trims if one or more cylinders have knock control active.

Ignition related imbalance between cylinders? Maybe on an old engine with oil pump driven distributor...I doubt I have any noticeable ignition imbalance in my engine with full sequential ignition. If you think so, please explain why that would be. But, it is obvious that the intake design with different length runners and shapes will give intake imbalance/air imbalance...and I think EGT will spot that nicely?

It's clear you never even looked at lambda's of individual cyls to make that statement. I have 8 on my engine and every intake runner and exhaust is almost identical. I still have imbalances. Difficult to assess what is the reason. A lot of factors come into play. But I do see an influence due to adding, retarding timing. A lot of items play a role in how a charge burns in a cylinder. Faster burning charge means more pressure, more pressure means faster moving exhaust gasses, which means more effect on the incoming charge during valve overlap, which...changes VE of that cilinder.

EGR's as a way to tune fuel doesn't do its job well imo, but like said before it's all up to you.

Yves wrote:It's clear you never even looked at lambda's of individual cyls to make that statement. I have 8 on my engine and every intake runner and exhaust is almost identical. I still have imbalances. Difficult to assess what is the reason. A lot of factors come into play. But I do see an influence due to adding, retarding timing. A lot of items play a role in how a charge burns in a cylinder. Faster burning charge means more pressure, more pressure means faster moving exhaust gasses, which means more effect on the incoming charge during valve overlap, which...changes VE of that cilinder.

I don't quite follow you I'm afraid. So you have individual EGOs on your V8? Do you also have EGTs installed and you are seeing imbalances between cylinder EGTs even though lambda has been matched? I am genuinely interested why you think there may be ignition timing imbalances between cylinders? A modern electronically controlled ignition system should be able to consistently deliver spark to all cylinders within at least 0.1° accuracy. If that isn't being acheived then there is something wrong and carrying out any form of performance tuning would be a waste of time until the timing issue is resolved.

Yves wrote:It's clear you never even looked at lambda's of individual cyls to make that statement. I have 8 on my engine and every intake runner and exhaust is almost identical. I still have imbalances. Difficult to assess what is the reason. A lot of factors come into play. But I do see an influence due to adding, retarding timing. A lot of items play a role in how a charge burns in a cylinder. Faster burning charge means more pressure, more pressure means faster moving exhaust gasses, which means more effect on the incoming charge during valve overlap, which...changes VE of that cilinder.

I don't quite follow you I'm afraid. So you have individual EGOs on your V8? Do you also have EGTs installed and you are seeing imbalances between cylinder EGTs even though lambda has been matched? I am genuinely interested why you think there may be ignition timing imbalances between cylinders? A modern electronically controlled ignition system should be able to consistently deliver spark to all cylinders within at least 0.1° accuracy. If that isn't being acheived then there is something wrong and carrying out any form of performance tuning would be a waste of time until the timing issue is resolved.

The issue is not what the ignition system can deliver but rather the different VE on the different cylinders. This VE difference also results in different ignition timing requirements leading to different EGTs even with the same AFR. There is also the amount of hot gases which varies with the different VEs which has an impact on EGTs. At least that's what I understand from the posts.

Yves wrote:It's clear you never even looked at lambda's of individual cyls to make that statement. I have 8 on my engine and every intake runner and exhaust is almost identical. I still have imbalances. Difficult to assess what is the reason. A lot of factors come into play. But I do see an influence due to adding, retarding timing. A lot of items play a role in how a charge burns in a cylinder. Faster burning charge means more pressure, more pressure means faster moving exhaust gasses, which means more effect on the incoming charge during valve overlap, which...changes VE of that cilinder.

I don't quite follow you I'm afraid. So you have individual EGOs on your V8? Do you also have EGTs installed and you are seeing imbalances between cylinder EGTs even though lambda has been matched? I am genuinely interested why you think there may be ignition timing imbalances between cylinders? A modern electronically controlled ignition system should be able to consistently deliver spark to all cylinders within at least 0.1° accuracy. If that isn't being acheived then there is something wrong and carrying out any form of performance tuning would be a waste of time until the timing issue is resolved.

The issue is not what the ignition system can deliver but rather the different VE on the different cylinders. This VE difference also results in different ignition timing requirements leading to different EGTs even with the same AFR. There is also the amount of hot gases which varies with the different VEs which has an impact on EGTs. At least that's what I understand from the posts.

Ok interesting. Just earlier in the thread you had mentioned never having used EGT so that confused me. Can I ask what sort of EGT deltas you are getting across all cylinders at full load when AFR is consistent?

Ok interesting. Just earlier in the thread you had mentioned never having used EGT so that confused me. Can I ask what sort of EGT deltas you are getting across all cylinders at full load when AFR is consistent?

I do my analysis on the basis of my EGO's which display the resulting VE change.

You have been implying that EGO is the only way to go for balancing and that EGT is no good for this due to ignition imbalances but if you do not have both systems installed in an engine to demonstrate that you still get EGT deltas with matched Lambda between cylinders then its all just speculation. I would be very interested if anybody had any data from their engine (steady state) to show that cylinder balancing using EGTs can result in some errors and to quantify these errors.

motthomas wrote:OK I get that. Do you have EGTs installed in your engine also?

You have been implying that EGO is the only way to go for balancing and that EGT is no good for this due to ignition imbalances but if you do not have both systems installed in an engine to demonstrate that you still get EGT deltas with matched Lambda between cylinders then its all just speculation. I would be very interested if anybody had any data from their engine (steady state) to show that cylinder balancing using EGTs can result in some errors and to quantify these errors.

You were very well aware that I only have EGO's. I have stated that before. So why do you ask. My point of view is that they are useless in tuning/waste of money and apparently I'm not the only one.

The whole timing imbalance is being blown out of proportion. There is no instance that I can think of that I would individually adjust ignition timing by cylinder. Find the sweet spot via mbt and leave it. Use egt or ego to check for cyl balance and adjust appropriately. I have seen the same results using both and egt is easier and cheaper. Usually the tuning window is wide enough that exact balance isn't necessary. Multiple ego on turbo cars is a pain due to pressure compensation issues. Even on a max effort install egt it more reliable and repeatable.

One example of when different timing is needed is the (stock) BBC. Two ports on each head flow in towards the center of the combustion chamber. Two flow out towards the cylinder wall. It is really two different V-4 engines with a common crank. Even if you could get the total flow (VE) to be the same for all cylinders, all that messy combustion stuff like turbulence/squish/quench/plug location make the two "sets" of cylinders require different timing and probably AFR/EGT to get the best power and efficiency. All this can be tweaked in perfectly with many happy (and expensive) hours on a brake-type dyno.

Paul_VR6 wrote:... Even on a max effort install egt it more reliable and repeatable.

I'm curious to know if you meant for that for turbo engines or for any engine. I ask because I know that Scott Clark was using individual EGO at the engine masters competition and that is definitely the place to use the best option (even if it has very little to do with real applications). But that was for N/A engines and I'm aware of the turbo engine constraints.

billr wrote:One example of when different timing is needed is the (stock) BBC. Two ports on each head flow in towards the center of the combustion chamber. Two flow out towards the cylinder wall. It is really two different V-4 engines with a common crank. Even if you could get the total flow (VE) to be the same for all cylinders, all that messy combustion stuff like turbulence/squish/quench/plug location make the two "sets" of cylinders require different timing and probably AFR/EGT to get the best power and efficiency. All this can be tweaked in perfectly with many happy (and expensive) hours on a brake-type dyno.

To add to this : take individual stacks where one cylinder starts to rob air from other cyls and add exhaust pulses that fire in the same exhaust header collector shortly after eachother where other pulses are 180° out and you will have an effect on VE of some cylinders where one will be lean and the other rich. We all know that rich mixtures burn faster and leaner mixtures burn slower. So I wonder why one could reason that individual cylinder timing requirements would all be the same. This is not taking into account minute chamber size differences, differences in flow due to airboxes, one cylinder that runs hotter than the other,....

Yves wrote:You were very well aware that I only have EGO's. I have stated that before. So why do you ask. My point of view is that they are useless in tuning/waste of money and apparently I'm not the only one.

I asked because your earlier (and later), quite definitive statements about how useless EGTs are for doing the job of cylinder matching implied that you do have direct experience with it. Without this experience, the advantages of EGO tuning vs EGT tuning you have put forward are total speculation without any basis in fact. To Paul's point, the difference in ignition timing is a total non-issue if you are dealing with any properly working, electronic ignition system.

If you do have different VE between cylinders then even matching the Lambdas with an individual EGO system will not make everything perfect. The cylinders will still have a loading imbalance due to the different masses of air and fuel being burned in each cylinder. Whether or not that is noticeable from a power or driveability perspective is another thing. Hence Bill's point about the BBC needing a lot of dyno time to set up right if you feel that it is worthwhile. At the end of the day, cylinder balancing is a fine-tuning exercise and an individual needs to decide if the benefits of the exercise are worth the time and cost of doing it and/or how far to take the exercise. EGT and EGO are both ways of achieving the same goal both with their own advantages & disadvantages and I for one could not justify any of the advantages that the EGO system gives purely due to the significant increase in cost.

As I see it, these are the main pros & cons of each system. Feel free to correct me or add any additional points.

EGOPros

Accuracy. Potentially more accurate. However I have no direct experience or data to say whether it is or is not and it would be very interesting to see supporting data.

Ease of calibration. Calibration can be carried out automatically using the ECU closed loop EGO control.

Calibration time. Less time required to dial in as the Lambda readings can you how much adjustment is required

Stabilisation time. Potentially faster stabilisation time due to less reliance on gas and sensor temperature stabilisation

Sensor Placement. Less sensitive to position along the exhaust. Sensors do not all need to be placed at the same distance from the exhaust valve to provide useable readings. However, do need to observe certain orientation guidelines to help sensor reliability.

Ignition timing sensitivity. Less sensitive different ignition timing so can be used for fuel trims while knock control is active.

Cons

Day 1 cost. At current Megaspartan costs, a 4 cylinder system costs c.£500 and an 8 cylinder system costs c.£950 (the cost of an MS3 Pro ECU!). Buying individual controllers and sensors could save a little cash but it does not make it cheap

Reliability. Generally, lambda sensors used with aftermarket controllers are less reliable than when used with OEM hardware. Lambda sensors are also sensitive to condensation and unburnt fuel (read alcohol fuelled engines) and higher gas temperatures if running closer to exhaust valves than recommended is likely to shorten sensor life.

Not suitable for turbocharged engines. Due to sensor inaccuracies at higher pressures.

EGTPros

DIY-able controller. With not a lot of difficulty, an Arduino type microcontroller can be used in conjunction with thermocouple amplifiers to read the temperatures and either log, display or pass to ECU EGT readings

Day 1 cost. If DIYed, a 4 cylinder controller and sensors can be had for c.£130. Add c.£20 per additional sensor for more cylinders or turbo inlet. More money can be spent on fancier motorsport orientated sensors if desired.

Reliability. Thermocouples really only fail due to vibration or overtemperature. Condensation in exhaust or unburnt fuel will not affect the reliability. Overtemperature for a k-type is also +1000°C which a gasoline engine should not experience under normal running conditions.

Maintenance costs. Failed EGT sensors can be replaced for c.£13 if using basic thermocouples.

Space. Thermocouple fittings are much smaller than Lambda bosses. Typical sizes for standard 3mm & under K-types are 1/8"BSP thread. Thermocouples can also be bent as soon as they exit the fitting and routed wherever is convenient. Even in a tight engine bay, thermocouple installation should not pose much of a challenge.

Flexibility. As well as fuel trims, EGT is also useful to monitor exhaust port gas temperatures at higher speeds and loads to help fuel calibration and to monitor turbine inlet temperatures in turbo applications.

Not pressure sensitive. There is no difference in reading EGT on an NA from a turbo engine.

Cons

Accuracy. Potentially less accurate than EGO but same caveat as first point. K-types are generally accurate to +-2°C which is more than accurate enough in an exhaust application.

Ease of calibration. Fuel trim calibration must be done manually.

Calibration time. More time required to dial in as the EGT delta does not indicate how much trim is required.

Stabilisation time. Thermocouples take time to reach thermal equilibrium in a transient gas flow. Smaller diameter sensors can improve this at the cost of reliability. Motorsports orientated sensors usually are designed for minimum stabilisation time and maximum reliability but cost more.

Sensor Placement. All sensors must be placed an equal distance from the exhaust ports to give useable comparative readings. Position along the exhaust is also important if using for limit monitoring so closer the the port is better. However, the sensors can be orientated any way around the pipe.

Ignition timing sensitivity. EGT is sensitive ignition timing so cannot be used to trim fuel while knock control is active.

Of all the disadvantages you list for WB sensors I haven't seen one of them and I'm using them since several years now. One exception to the rule is the fitting in thight spaces, however you also have that to deal with in terms of EGT sensors and more : they definately have to be at equal distance from the head and preferably very close to it, a disadvantage you don't have with a WB. As far as calibration is concerned, the LSU4.9 doesn't need to be calibrated anymore. In terms of EGT's I only see one advantage and that is in case of a turbo engine where you want to protect your engine from melting down. As a tuning device for fuel, you have the problem that temps go up on both sides of stoich which gives a problem and a lot more calibration issues to get the right fuel.But I guess all the oem's are using the expensive WB's for absolutely no reason

Anyway I don't see any use trying to convince you. You use whatever you see fit, I don't care.

Last edited by Yves on Fri Jan 05, 2018 1:06 pm, edited 1 time in total.

You can use per-cylinder EGO on turbo engines. You can use pressure compensated controllers but you have to be careful about the heat issue: you need to locate the sensors appropriately and possibly use heat sinks. And, of course, you need to add a pressure sensor. Another solution is the use of sampling chambers where tubing is used to bring exhaust gases to a remotely located sensor; that deals with both pressure and temperature issues.

You could also ignore the pressure compensation if you simply want to balance fueling: all sensors will be similarly affected by the exhaust backpressure. You can then rely on a single after-turbo EGO to get the correct overall AFR. That wouldn't be a worse solution that using EGT (ignoring cost and complexity) where you also rely an even more indirect measurement of AFR.

Jean

EDIT: Having said that, I do agree that each solution has its own set of pros and cons and depending on your own priorities and preferences, one setup will better for you. I think you can have good results with either but you need to do your homework before choosing and once you start tuning.